hybrid – Anole Annals

Photo by James Stroud

At JMIH 2016, I chatted with Johanna Wegener, a graduate student at the University of Rhode Island in Jason Kolbe’s lab, about her poster detailing her work identifying hybridization between Anolis carolinensis and A. porcatus in southern Florida.

Interspecific hybridization in anoles is thought to be fairly rare, with the best-known example being hybridization between Anolis carolinensis (native to the southeastern U.S.) and A. porcatus (native to Cuba) in southern Florida. I was surprised to learn how little we know about this rumored hybrid zone.

A. porcatus was likely introduced into Florida within the last few decades, but the striking morphological similarities between A. carolinesis and A. porcatus make anecdotal reports of hybridization hard to confirm. Wegener conducted the first genetic analyses of hybridization between A. carolinesis and A. porcatus. She genotyped 18 nuclear microsatellites from green anoles in Florida (Palm Beach and South Miami) and western Cuba and conducted a STRUCTURE analysis and found support for three genetic clusters consisting of Cuban A. porcatus, and two Floridian groups (one from Palm Beach and one from South Miami). With the addition of the mitochondrial ND2 marker, she found that the South Miami population had both A. carolinensis and A. porcatus haplotypes. Interestingly, there appeared to be very few recent hybrids; instead, the hybrid group appeared distinct from either parent group, suggesting that hybridization has been occurring for several generations.

In addition, Wegener looked at the variation in A. porcatus and A. carolinensis markers in each hybrid individual and found examples of some parent markers being retained at high proportions in the hybrids, possibly suggesting the retention of beneficial parent alleles in the hybrids.

Given that this study was only conducted at two sites in Florida, the exciting next step of this study is to better quantify the genetic makeup of hybrids across southern Florida and map out the hybrid zone.

Dewlap variation in Anolis distichus in Hispaniola. The photos at the bottom show the change in dewlap color along the two transects in the recent study by Ng and Glor.

Despite all of the research on anole evolution conducted in the last 40 years, one important question still eludes us: how does speciation in anoles occur? This, of course, is of fundamental importance, because the great species richness of these lizards implies that speciation has run rampant in this group. So, we’d like to know why.

We don’t know much about speciation in anoles, but we do know a little. First, it is thought that the dewlap plays an important role. Sympatric anole species almost never have identical dewlaps, and experimental and observational evidence suggests that anoles use their dewlaps for species-recognition. Hence, understanding anole speciation may, to a significant extent, reduce to understanding the factors that cause populations to evolve differences in their dewlaps.

A different perspective on anole speciation relates to the classic question of whether allopatry is necessary or whether, as suggested by many recent studies, natural selection driving differentiation—whether in allopatry or not—is a more important stimulus to genetic differentiation. Recent work in the Lesser Antilles by Thorpe and colleagues has argued that environmental differences are the primary drivers of genetic differentiation within anoles, a result also suggested by Leal and Fleishman’s studies on A. cristatellus in Puerto Rico.

In this light, perhaps the most enigmatic anole is Anolis distichus of Hispaniola.